Jim O’Mahoney, shown in a 1970s photo, is the subject of a documentary, “Signal Hill Speed Run,” about skateboard racing. The film screens tonight as part of the Santa Barbara International Film Festival.

“It was the X-Games of its day,” he says.

These days Jim O’Mahoney is best known to Santa Barbarans as the owner of the Surf Museum on Helena Avenue and its newer, but equally delightful, history museum next door.

But back when he was 30, Mr. O’Mahoney started a four-year event at the same time as the modern skateboard industry, resulting in some incredible speeds and dangerous accidents.

A lot of this might have been forgotten by most, except for those who were there.

But “Signal Hill Speed Run,” a new documentary that just premiered at the Santa Barbara International Film Festival — and gets a repeat showing tonight — has brought the event back for new generations to share.

The Signal Hill Speed Run was a scarifying downhill race at one of the steepest hills in the city of the same name, near Long Beach. Skateboarders would stand and head straight down this vertiginous drop, achieving speeds as high as 50 mph — if they stayed on their boards.

To go faster, following years’ contestants saw contestants crouching or in a luge position. Then the aerodynamic shells came out. But due to serious injuries, constant ambulance rides and insurance issues, the event stopped in 1980.

Mike Horelick and Jon Carnoy assembled the film from modern-day interviews with the participants, including Mr. O’Mahoney, photographs, and amazing old film footage that look like outtakes from a California “Dazed and Confused.” (The fashion, of course, is amazing, as is the hair.)

Musician and skateboarder Ben Harper narrates.

Mr. O’Mahoney, now 67, had already started the U.S. Skateboard Association and was running contests here and in Ventura in 1975. David Frost from ABC approached Mr. O’Mahoney for a Guinness Book of World Records program — could he arrange an event to set a world record for downhill speed? And could he organize it in three weeks?

“I knew immediately where to go,”

Mr. O’Mahoney says. “I grew up in Long Beach and Signal Hill was the huge bump in the middle of the city.” As a kid he went bombing down it on his bike.

There had already been a competition years earlier — a Model T hill climb to see what could make it to the top. But going down was easier, and scary.

The first year, Mr. O’Mahoney only needed a few contestants to satisfy the network and set the record. But the next year, “here they all came!” he says.

As the film shows, the event was a raucous party, with people lined up and down the hill behind very flimsy safety barriers. Anybody could take part, including one drunk guy on a Big Wheel.

Hay-bale barriers at the bottom didn’t stop some of the racers. Bones were broken. The phrase “breakneck speed” was not just hyperbole. Nobody filed suit, however.

After the event shut down, Mr. O’Mahoney continued promoting races and publishing Skateboard Magazine. He continued to enter surf competitions, even winning one at age 48. And his collector’s mentality led to the Surfing Museum in 1992, which boasts classic boards and memorabilia.

These days, Mr. O’Mahoney says he’d never be able to put on such an event as seen in the film. Too much liability. But he does have some places in mind where he’d like to do a new run. He’s just not saying where.

Right now, the speed record is held by Mischo Erban at 80.74 mph.

The legacy of the Speed Run can be seen in events like the X-Games and in the endless stream of craziness seen on YouTube. Young guys are “made of rubber” and will keep seeking adrenaline rushes.

“We’re all shaved apes,” he says. “Man keeps getting pushed further up the ladder. It’s not going to stop. You think you’ve seen everything, but in a couple of years, someone will do something crazier.”